TSP G-Fund vs C-Fund vs Lifecycle: Federal Retiree Allocation

The Thrift Savings Plan is the largest defined-contribution retirement plan in the world, covering roughly 6.7 million federal employees and uniformed service members. It offers five individual funds and a series of target-date Lifecycle funds — and most participants default into the L Fund assigned to their age cohort without ever analyzing whether that allocation matches their actual retirement income needs. The three funds that matter most for the allocation decision are the G Fund (government bonds, ~2.3% historical annualized return), the C Fund (S&P 500 index, ~10.4% historical annualized return), and the Lifecycle funds (blended, ~7% to 9% depending on target date and time period). Every other TSP decision — when to withdraw, how much to convert to Roth, whether to roll to an IRA — flows downstream from this allocation choice.

The three funds: what you are actually buying

G Fund: principal guarantee, inflation drag

The G Fund invests in a non-marketable US Treasury security issued specifically to the TSP. Its interest rate is reset monthly to the weighted average yield of all outstanding Treasury notes and bonds with 4+ years to maturity. You cannot lose principal in any pay period — the G Fund has never posted a negative monthly return since the TSP’s inception in 1987. Over the 20 years ending December 2025, the G Fund returned approximately 2.3% annualized. With CPI inflation averaging 2.5% to 3.0% over that same period, the G Fund’s real (after-inflation) return has been approximately zero. It preserves purchasing power in nominal terms but does not grow it.

The G Fund is appropriate for money you will spend within 1 to 3 years, or as a ballast allocation during the first few years of retirement when sequence-of-returns risk is highest. It is not appropriate as a 100% allocation for a retirement that may last 25 to 30 years.

C Fund: long-term growth engine with real drawdown risk

The C Fund tracks the S&P 500 index through a separate account managed by BlackRock (expense ratio: 0.049% as of 2025, among the lowest in any retirement plan). Over the 20 years ending December 2025, the C Fund returned approximately 10.4% annualized. It lost 37% in 2008, 20% in 2022, and has experienced intra-year drawdowns exceeding 10% roughly one in every three years. For a federal employee 15+ years from retirement, the C Fund’s compounding power is the primary wealth-building tool in the TSP.

The risk of the C Fund is not that it loses money — the S&P 500 has recovered from every historical drawdown — but that it loses money at the wrong time. A 30% drawdown in year one of retirement, combined with ongoing withdrawals, can permanently impair a portfolio. This is sequence-of-returns risk, and it is the reason retirees cannot hold 100% C Fund regardless of time horizon.

Lifecycle funds: automatic glide path, generic assumptions

The L Funds blend all five TSP funds (G, F, C, S, I) and automatically shift from stocks to bonds as the target date approaches. An L 2035 fund might hold 65% stocks (C+S+I) and 35% bonds (G+F) today, gradually shifting to 80%+ bonds by 2035. After reaching the target date, the fund rolls into L Income, which holds approximately 74% G Fund, 6% F Fund, and 20% stocks — a conservative allocation designed for someone already withdrawing.

The advantage is simplicity. The disadvantage is that the glide path assumes a generic retiree with no pension and average risk capacity. Federal retirees under FERS have a guaranteed pension and Social Security — two bond-like income streams that most private-sector retirees do not have. This means the L Fund’s shift toward the G Fund may be more conservative than a FERS retiree actually needs, particularly if the pension and Social Security already cover most essential expenses.

The opportunity cost of over-allocating to the G Fund: worked examples

The following table shows the projected balance from contributing $400/month into each fund over different time horizons, using historical annualized returns. These are historical averages, not guarantees — actual returns will vary, and past performance does not predict future results.

At age 35, the difference between 100% G Fund and 100% C Fund over 27 years is approximately $325,000 on identical $400/month contributions. The L 2050 fund captures roughly 65% of the C Fund’s upside while dampening volatility through diversification. At 5 years to retirement, the gap narrows to roughly $5,800 — illustrating why the allocation question matters most for those with a long time horizon and matters least for those about to retire.

These figures use the future-value-of-annuity formula: FV = PMT × [((1+r)ⁿ − 1) / r], where r is the monthly rate and n is the number of months. Historical returns are from TSP.gov fund performance data through December 2025. Actual future returns will differ.

The FERS pension offset: why federal retirees can hold more stock

This is the dimension that generic TSP advice misses entirely. A FERS retiree with 30 years of service and a high-3 average salary of $120,000 receives an annuity of approximately $36,000/year (1.1% × 30 × $120,000 for retirement at age 62 or later, reduced if earlier). Add Social Security at full retirement age — say $30,000/year — and the retiree has $66,000 in guaranteed annual income, adjusted for inflation (full COLA on Social Security, partial on FERS).

If essential expenses total $72,000/year, the TSP only needs to produce $6,000/year to close the gap. A $500,000 TSP balance at a 1.2% withdrawal rate is barely being tapped. This retiree can afford to hold 60% to 80% in the C and S Funds — far more aggressive than the L Income fund’s 20% stock allocation — because the pension and Social Security have already built the income floor. The TSP functions as a growth portfolio and Roth conversion reservoir, not as the primary income source.

Contrast this with a private-sector retiree who has no pension, depends on a 401(k) for 50%+ of retirement income, and must protect against sequence-of-returns risk from day one. That retiree needs significantly more bond exposure. The L Fund’s glide path is designed for the private-sector scenario — not for someone with a FERS annuity.

Allocation framework by age cohort

Age 30s to mid-40s: 15+ years to retirement

Time horizon favors maximum equity exposure. A 80% C Fund / 10% S Fund / 10% I Fund allocation (or even 100% C Fund for aggressive accumulators) historically outperforms any other TSP combination over 15+ year periods. The G Fund serves no purpose at this stage — the monthly paycheck provides current income, and the TSP’s sole job is to compound. An L 2050 or L 2055 fund captures most of the growth but introduces international and bond drag that reduces returns by 1 to 3 percentage points annually. For those comfortable monitoring their allocation annually, individual fund selection outperforms the Lifecycle default.

5 to 15 years from retirement: the transition zone

This is where the allocation question becomes genuinely difficult. You have enough time for equities to recover from a drawdown, but a 40% crash 3 years before retirement would be painful. The framework: calculate your FERS annuity and projected Social Security (use SSA.gov’s my Social Security tool). Subtract guaranteed income from essential expenses. The resulting gap is what the TSP must cover in early retirement.

If the gap is small (under $15,000/year), you can maintain 60% to 70% C/S Fund exposure because you are not relying on the TSP for baseline income. If the gap is large (over $30,000/year), consider shifting 2 to 4 years of the gap amount into the G Fund as you approach retirement — effectively building a “cash bucket” inside the TSP to cover early withdrawals without selling equities in a downturn. An L Fund with a target date near your retirement year accomplishes a similar shift automatically, but may over-allocate to the G Fund relative to your actual gap.

Within 5 years of retirement or already retired

Sequence-of-returns risk is real and front-loaded in the first 5 years of withdrawals. The standard approach: hold 2 to 4 years of planned TSP withdrawals in the G Fund, with the remainder in C/S/I for continued growth. If your FERS pension and Social Security cover 90%+ of essential expenses (common for 30-year FERS employees), even a retiree can justify 50% to 70% in equities because TSP withdrawals are discretionary, not mandatory (until RMDs begin).

The L Income fund’s 74% G Fund / 20% stocks allocation is appropriate only if the TSP is your primary income source. For most FERS retirees, it is far too conservative.

Worked example: Maria, GS-14, age 60, $620,000 TSP balance

Maria is a GS-14 with 28 years of FERS service and a high-3 average salary of $128,000. She plans to retire at 62. Her FERS annuity: 1.1% × 28 × $128,000 = $39,424/year. She will receive a FERS supplement (approximating Social Security) of roughly $18,000/year until age 62 becomes the MRA+30 eligibility, then transitions to actual Social Security. She plans to delay Social Security until 67 (FRA), at which point her benefit is approximately $32,000/year.

Current TSP balance: $620,000 (100% traditional, currently 40% G Fund / 30% C Fund / 15% S Fund / 15% L 2030 — a common “set it and forget it” allocation from years ago). Essential expenses: $78,000/year. Discretionary: $18,000/year. Total need: $96,000/year.

Ages 62–67: pre-Social Security gap

Guaranteed income: FERS annuity $39,424 + FERS supplement ~$18,000 = $57,424. Gap: $96,000 − $57,424 = $38,576/year from the TSP. Over 5 years, Maria needs approximately $193,000 from the TSP to bridge to Social Security.

Recommended reallocation at age 60: move $200,000 (approximately 32% of TSP) into the G Fund to cover 5 years of withdrawals plus a buffer. Allocate the remaining $420,000 as 75% C Fund / 15% S Fund / 10% I Fund for growth. This keeps $420,000 growing at the TSP’s equity return while ensuring the bridge years are fully funded regardless of market conditions.

Ages 67–73: Social Security starts, pre-RMD Roth window

Once Social Security begins at 67, Maria’s guaranteed income rises to $39,424 + $32,000 = $71,424. The gap drops to $96,000 − $71,424 = $24,576/year. The TSP’s equity allocation has (historically) grown the $420,000 to approximately $580,000 to $650,000 over 5 years at ~8% annual returns.

This is Maria’s prime Roth conversion window. Her taxable income is relatively low: $39,424 (FERS, fully taxable) + ~$27,200 (85% of SS taxable) = ~$66,600 in AGI before TSP withdrawals. She can withdraw $24,576 for spending and convert an additional $30,000 to $40,000 to a Roth IRA while staying below the 2026 IRMAA married-filing-jointly threshold of approximately $212,000 (or the single threshold of ~$106,000 if unmarried). Each dollar converted reduces future RMDs and their associated tax liability.

Age 73+: RMDs begin

At age 73, Maria must take RMDs from her traditional TSP (or traditional IRA if she rolled over) per IRC Section 401(a)(9). If her traditional balance is $500,000 at 73, her first-year RMD is approximately $18,870 (using the Uniform Lifetime Table divisor of 26.5). If she has converted aggressively during ages 67 to 72, the remaining traditional balance — and therefore the RMD — is smaller, keeping her in a lower bracket and potentially below IRMAA thresholds.

At this stage, the allocation depends on how much of the TSP Maria is spending versus preserving. If RMDs exceed her spending needs (common if she converted aggressively and reduced the traditional balance), she can reinvest the excess in a taxable brokerage account. The TSP equity allocation can remain at 50% to 60% C/S Fund because the pension and Social Security still cover the income floor.

Tax interactions most TSP guides skip

RMDs under SECURE 2.0

Traditional TSP balances are subject to RMDs beginning at age 73 (age 75 for those born in 1960 or later) under IRC Section 401(a)(9) as amended by SECURE 2.0. Roth TSP balances held inside the employer plan are also subject to RMDs — this is a critical distinction. To avoid RMDs on Roth money, you must roll the Roth TSP to a Roth IRA after separation from service. The penalty for missing an RMD is 25% of the shortfall (reduced from 50% by SECURE 2.0), or 10% if corrected within two years. If you are still employed by the federal government past age 73, the still-working exception allows you to defer TSP RMDs until you actually separate.

IRMAA bracket management

Medicare Part B and Part D premiums increase at IRMAA income thresholds, based on MAGI from two years prior. In 2026, the first IRMAA surcharge begins at approximately $106,000 MAGI (single) or $212,000 (married filing jointly). A large TSP withdrawal or Roth conversion in 2024 could trigger IRMAA surcharges in 2026. For Maria, withdrawing $38,576 for spending plus converting $35,000 to Roth produces roughly $140,000 in AGI ($66,600 base + $38,576 + $35,000) if single — above the first IRMAA threshold by approximately $34,000, adding roughly $1,040/year to her Medicare premiums. Splitting the Roth conversion across two years or timing conversions to years when other income is lower can keep her below the cliff.

Withdrawal sequencing: TSP vs Roth vs taxable

The conventional wisdom — withdraw from taxable first, then tax-deferred, then Roth last — does not account for the Roth conversion window. A more tax-efficient sequence for federal retirees: spend from the G Fund bucket (traditional TSP) for living expenses while simultaneously converting additional traditional TSP to Roth IRA up to your target bracket. After age 73, let RMDs satisfy spending needs first, then supplement from Roth (tax-free) if needed. The Roth IRA grows tax-free, has no RMDs for the original owner, and passes to heirs under the 10-year rule with no income tax until distributed — making it the most valuable account to preserve.

Common mistakes federal retirees make with TSP allocation

• 100% G Fund at retirement. The most common mistake. A $500,000 portfolio at 2.3% nominal returns barely keeps up with inflation. If retirement lasts 25 to 30 years, the real value of that portfolio declines every year. The FERS pension already functions as a bond — doubling down on bonds inside the TSP provides safety you do not need at the cost of growth you do.
• Ignoring the Roth TSP rollover. Roth TSP balances are subject to RMDs inside the employer plan. Rolling to a Roth IRA after separation eliminates this requirement entirely. Many retirees leave Roth TSP balances in the plan and unknowingly take distributions they could have avoided.
• Using the L Income fund by default. The L Income fund’s 74% G Fund allocation assumes the TSP is your only retirement asset. With a FERS pension and Social Security, most retirees have 70% to 90% of essential expenses covered by guaranteed income — the TSP should lean toward growth, not more bonds.
• No Roth conversion strategy in the gap years. The period between FERS retirement and age 73 is the lowest-income window most federal employees will ever experience. Failing to convert traditional TSP to Roth during this window means paying higher taxes on larger RMDs later, potentially triggering IRMAA surcharges that a systematic conversion strategy would have avoided.
• Withdrawing from the wrong fund first. TSP allows you to specify withdrawals proportionally across all funds (default) or from a specific fund. Withdrawing proportionally sells C Fund shares in a downturn. Instead, set withdrawals to come from the G Fund during market declines, preserving equity shares for recovery.

Key takeaways

• The G Fund guarantees principal but has returned approximately 2.3% annualized over 20 years — barely matching inflation. Over 27 years of $400/month contributions, the difference between 100% G Fund ($155,000) and 100% C Fund ($480,000) is approximately $325,000. This opportunity cost is the single most important number in the TSP allocation decision. The G Fund has a role as a near-term spending buffer, but not as a long-term growth allocation.
• Federal retirees under FERS have a structural advantage that generic TSP advice ignores: the FERS annuity and Social Security function as a bond allocation outside the TSP. A 30-year FERS employee with a $120,000 high-3 salary has approximately $66,000/year in guaranteed income — covering 80% to 90% of most essential expense budgets. This pension offset means the TSP can lean heavily toward equities (C and S Funds) even in retirement, because it is not the primary income source.
• The Lifecycle L Income fund’s 74% G Fund allocation is designed for retirees with no pension. For FERS retirees whose pension and Social Security cover most expenses, L Income is significantly more conservative than necessary. A custom allocation — 2 to 4 years of withdrawals in the G Fund, remainder in C/S/I Funds — preserves growth potential while managing sequence-of-returns risk.
• The post-retirement, pre-RMD years (typically ages 62 to 73 for FERS retirees) are the optimal Roth conversion window. Rolling traditional TSP to a traditional IRA after separation, then converting to Roth up to the top of the 22% or 24% bracket each year, reduces future RMDs, lowers lifetime tax liability, and avoids IRMAA surcharges. Roll the Roth TSP to a Roth IRA immediately after separation to eliminate Roth TSP RMDs.
• Use the G Fund as a spending bucket, not a portfolio strategy. Set TSP withdrawals to come from the G Fund during market downturns (rather than the default proportional withdrawal across all funds), hold 2 to 4 years of planned withdrawals in the G Fund at all times, and let C/S/I Fund allocations ride through volatility. This “bucket strategy” inside the TSP captures equity upside while ensuring you never sell stocks at a loss to fund living expenses.